1. Field of the Invention
The present invention relates to a vacuum thermal insulating panel wherein a thermal insulating material is vacuum-packed in a sealing bag composed of an obverse face material and a reverse face material, and a method for preparing the same. More specifically, this invention concerns a vacuum thermal insulating panel capable of preventing gas permeation from the outside, reflecting heat, and reducing thermal conduction along the outer surface thereof, and a method for preparing the same.
2. Description of the Prior Art
Conventionally, as a vacuum thermal insulating panel, there has been disclosed a method for manufacturing a thermal insulating panel in Japanese Patent Laid-open No. Sho 58-50394 (Method for Manufacturing Thermal Insulating Panel), wherein a thermal insulating panel is manufactured by the steps of: charging powder in a gas permeable packing bag; inserting it in an exterior bag, followed by sealing under vacuum. However, the above method has a disadvantage that, when the exterior bag is made of plastic, gas is liable to permeate from the surface of the exterior bag, thus degrading the vacuum degree (thereby increasing the thermal conductivity), and that, when a metal foil is laminated on the exterior bag for preventing gas permeation, the peripheral portion of the thermal insulating panel becomes thermal-conducting, thus degrading the thermal insulating performance.
To solve the above problem, the present applicant has proposed a method of forming an adhesion obstructing layer for obstructing adhesion of a metal foil at a portion to be thermal adhesive-bonded or a thermal adhesive-bonded portion of the exterior bag, and then cutting and removing the metal foil of the portion, as disclosed in Japanese Patent Laid-open No. Sho 62-39455 (Method for Manufacturing Packing Bag); however, this method has a difficulty in mass-production because of its complicated process.